Microblistering: What to do when your filler forms bubbles

Is your filler forming bubbles after application? Are microbubbles appearing on the surface? Discover all the solutions to this issue in this guide. Raphaël Estrella, Beissier’s technical advisor, explains the causes of microblistering—such as humidity, dust, improper filler application, and concrete outgassing—and demonstrates how to prevent it. Depending on the substrate, our expert provides tips to detect, minimize, and address this phenomenon effectively.

Understanding microblistering and how to combat it

The application environment plays a crucial role in the performance of a filler. Properly understanding, analyzing, and adapting to the environment is essential; otherwise, microblistering—characterized by the appearance of microbubbles after filler application—can occur.

What is microblistering?

Microblistering is a surface defect caused by trapped solvents within the filler. While there are various causes, solutions are always available. Raphaël Estrella, Beissier’s technical expert, breaks them down below.

Humidity

Humidity is a primary cause of microblistering. Identify and address the source of moisture (e.g., water damage, leaks) by installing ventilation or using products designed for the specific room conditions.

Dust

Dust on the substrate can lead to microbubbles. The solution is simple: dust off or wash the surfaces thoroughly before application.

Concrete Outgassing

Gas pockets escaping from concrete during filler application can result in microblistering. To prevent this, apply a primer to seal the concrete.

Overly Sealed Substrates

A substrate that is too sealed—often due to an overly rich primer—can lead to microbubbles. Use a suitable primer to address this.

After applying a primer, proceed with the filler. However, note that microblistering often occurs on overly sealed substrates with rich primers (not standard primers). When the substrate is too sealed, the filler cannot penetrate, and air pockets form between the substrate and filler, causing microbubbles.

To fix this, dry and scrape the affected areas, then apply a microporous primer or sand the surface to restore porosity and adhesion before reapplying filler.

Improper application on textured substrates

Incorrect application of filler on textured substrates can also cause microbubbles. Prevent this by eliminating trapped air:

• on the first pass, apply pressure with the blade to remove air.
• follow up with a second, thicker layer to ensure complete coverage.

Preventive measures

To avoid unpleasant surprises:

• Follow the recommended filler-to-water ratios provided on the packaging.
• Adhere to the specified drying times.
• Most importantly, thoroughly inspect and analyze your substrate before applying filler.

Remember: A well-prepared project means no microbubbles!